Coating technology

ABSTRACT

The present invention provides an aqueous platinum electroplating bath including: a) a source of platinum ions; and b) a source of polyphosphate anions, and wherein the bath has a pH in the range from about 2 to about 9 when it is in use or ready for use. The aqueous platinum electroplating bath may optionally include one or more levellers. The invention also provides the use of the platinum electroplating bath and platinum salts suitable for use in the bath.

The present invention concerns improvements in coating technology, more particularly it concerns improvements in the deposition of coatings of platinum by electroplating. Even more particularly, the present invention concerns improvements in the deposition of coatings of platinum by electroplating in a commercial or industrial process.

Electroplating is a well-known technique for applying coatings of platinum and other platinum group metals onto conductive substrates. Although most substrates for plating according to the present invention are conductive metals or graphite, composites incorporating conductive fibres or particles may be considered as well as plastics which have a keying metal deposit or flash coating. The coatings may be a thin “flash” coating used for jewellery, or several microns in thickness, generally up to about 20 μm, depending upon the intended use of the coated product; the coating may be thicker for certain applications. There are a number of major uses for functional (including protective as well as catalytic coatings) or decorative coatings, in jewellery, in electronics for depositing layers for memory applications or conductive tracks, and in the coating of turbine blades, where a platinum coating is used in the formation of protective aluminides. Two major types of ammoniacal platinum plating baths have been introduced by Johnson Matthey in the last few decades, namely “P Salt” and “Q Salt®”. “P salt” is an ammoniacal solution of diammine dinitroplatinum(II), i.e. (NH₃)₂Pt(NO₂)₂. “Q Salt®” is an ammoniacal solution of tetraammineplatinum(II) hydrogen orthophosphate.

The teaching of EP0358375A is herein incorporated by reference in its entirety for all purposes. “Q Salt®” has been very successfully used in industry. Plating is carried out at temperatures of 90° C. or above. At such temperatures, water vapour and ammonia are driven off, with the consequential need to regularly replenish these components during plating in order to maintain plating rate. Additionally, the platinum salt needs to be replenished with use of the bath. There have been attempts to find alternatives to ammonia but there remains a need to find plating baths which are more environmentally friendly in reducing or eliminating the loss of toxic ammonia, and desirably which are less energy intensive and/or which offer other advantages, such as having a good plating rate, good coating properties and compatible with plating additives that improve coating properties.

Most platinum plating is carried out under significantly alkaline conditions. For certain substrates, for which alkaline conditions encourage oxide or hydroxide formation or cause other difficulties, it would be desirable to operate under acidic or neutral to mildly alkaline conditions.

SUMMARY OF THE INVENTION

The present invention relates to a platinum plating bath. The bath may be used successfully over extended periods and the platinum component may be replenished easily. In certain embodiments, the bath provides a safe, neutral, non-corrosive bath. In certain embodiments, the baths yield a bright and shiny plate. In certain embodiments, the baths may be used under relatively energy-efficient conditions. In certain embodiments, the baths have a good plating rate providing a good deposition of platinum in a reasonable period of time. In certain embodiments and, depending on the platinum plating salt selected, the baths may be used without the emission of ammonia or with only low emissions.

In one aspect, the present invention provides an aqueous platinum electroplating bath comprising:

-   -   a) a source of platinum ions; and     -   b) a source of polyphosphate anions,         and wherein the bath has a pH in the range from about 2 to about         9 when it is in use or ready for use.

In another aspect, the invention provides the use of the aqueous platinum electroplating bath of the present invention for plating platinum or a platinum alloy onto a substrate.

In yet another aspect, the invention provides a platinum salt which is tetraammineplatinum(II) dihydrogen pyrophosphate, di[tetraammineplatinum(II)]pyrophosphate or Na₂[Pt(NH₃)₄][H₂P₂O₇].

DEFINITIONS

The point of attachment of a moiety or substituent is represented by “-”. For example, —OH is attached through the oxygen atom.

“Alkyl” refers to a straight-chain or branched saturated hydrocarbon group. In certain embodiments, the alkyl group may have from 1 to 10 carbon atoms, in certain embodiments from 1 to 8 carbon atoms, in certain embodiments from 1 to 6 carbon atoms. The alkyl group may be substituted or unsubstituted. Unless otherwise specified, the alkyl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable carbon atom. Typical alkyl groups include but are not limited to methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, and the like.

“Alkenyl” refers to a straight-chain or branched unsaturated hydrocarbon group having at least one carbon-carbon double bond. The group may be in either the cis- or trans-configuration around each double bond. In certain embodiments, the alkenyl group can have from 2 to 10 carbon atoms, in certain embodiments from 2 to 8 carbon atoms, in certain embodiments, 2 to 6 carbon atoms. The alkenyl group may be unsubstituted or substituted. Unless otherwise specified, the alkenyl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable carbon atom. Examples of alkenyl groups include but are not limited to ethenyl (vinyl), 2-propenyl (allyl), 1-methylethenyl, 2-butenyl, 3-butenyl and the like.

“Alkynyl” refers to a straight-chain or branched unsaturated hydrocarbon group having at least one carbon-carbon triple bond. In certain embodiments, the alkynyl group can have from 2-10 carbon atoms, in certain embodiments from 2-8 carbon atoms, in certain embodiments, 2-6 carbon atoms.

The alkynyl group may be unsubstituted or substituted. Unless otherwise specified, the alkynyl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable atom. Examples of alkynyl groups include but are not limited to ethynyl, prop-1-ynyl, prop-2-ynyl, 1-methylprop-2-ynyl, but-1-ynyl, but-2-ynyl, but-3-ynyl and the like.

“Aryl” refers to an aromatic carbocyclic group. The aryl group may have a single ring or multiple condensed rings. In certain embodiments, the aryl group can have from 6 to 20 carbon atoms, in certain embodiments from 6 to 15 carbon atoms, in certain embodiments, 6 to 12 carbon atoms. The aryl group may be unsubstituted or substituted. Unless otherwise specified, the aryl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable carbon atom. Examples of aryl groups include, but are not limited to, phenyl, naphthyl, anthracenyl and the like.

As used herein, “bath” includes a concentrate for ease of storage and transport.

“Cycloalkyl” refers to a cyclic saturated hydrocarbon group. In certain embodiments, the cycloalkyl group may have from 3-10 carbon atoms, in certain embodiments from 3-10 carbon atoms, in certain embodiments, 3-8 carbon atoms, in certain embodiments, 3-6 carbon atoms. The cycloalkyl group may be unsubstituted or substituted. Unless otherwise specified, the cycloalkyl group may be attached at any suitable carbon atom and, if substituted, may be substituted at any suitable atom. Typical cycloalkyl groups include but are not limited to cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and the like.

“Heterocycloalkyl” refers to a saturated cyclic hydrocarbon group wherein one or more carbon atoms are independently replaced with one or more heteroatoms (e.g. nitrogen, oxygen, phosphorus and/or sulfur atoms). The heterocycloalkyl group may have from 2-10 carbon atoms, in certain embodiments from 2-10 carbon atoms, in certain embodiments, 2-8 carbon atoms in certain embodiment, 2-6 carbon atoms. The heterocycloalkyl group may be unsubstituted or substituted. Unless otherwise specified, the heterocycloalkyl group may be attached at any suitable atom and, if substituted, may be substituted at any suitable atom. Examples of heterocycloalkyl group include but are not limited to epoxide, morpholinyl, piperadinyl, piperazinyl, thirranyl and the like.

“Heteroalkyl” refers to a straight-chain or branched saturated hydrocarbon group wherein one or more carbon atoms are independently replaced with one or more heteroatoms (e.g. nitrogen, oxygen, phosphorus and/or sulfur atoms). In certain embodiments, the heteroalkyl group may have from 1 to 10 carbon atoms, in certain embodiments from 1 to 8 carbon atoms, in certain embodiments from 1 to 6 carbon atoms. The heteroalkyl group may be unsubstituted or substituted. Unless otherwise specified, the heteroalkyl group may be attached at any suitable atom and, if substituted, may be substituted at any suitable atom.

“Heteroaryl” refers to an aromatic carbocyclic group wherein one or more carbon atoms are independently replaced with one or more heteroatoms (e.g. nitrogen, oxygen, phosphorus and/or sulfur atoms). In certain embodiments, the heteroaryl group can have from 5 to 20 carbon atoms, in certain embodiments from 5 to 15 carbon atoms, in certain embodiments, 5 to 12 carbon atoms. Unless otherwise specified, the heteroaryl group may be attached at any suitable atom and, if substituted, may be substituted at any suitable atom. Examples of heteroaryl groups include but are not limited to furanyl, indolyl, oxazolyl, pyridinyl, pyrimidinyl, thiazolyl, thiphenyl and the like.

“Heteroatom” refers to nitrogen, oxygen or sulfur, preferably nitrogen or oxygen and most preferably nitrogen.

“Polyphosphate” refers to a group comprising two or more (e.g. 3, 4, 5 or 6) phosphate (PO₄) groups linked together via shared oxygen atoms. The polyphosphate may be linear or cyclic.

“Room temperature” means from about 20° C. to about 35° C.

“Substituted” refers to a group in which one or more (e.g. 1, 2, 3, 4 or 5) hydrogen atoms are each independently replaced with substituents which may be the same or different. Examples of substituents include but are not limited to -halo, —C(halo)₃, —R^(a), ═O, ═S, —O—R^(a), —S—R^(a), —NR^(a)R^(b), ═NR^(a), ═N—OR^(a), —CN, —SCN, —NCS, —NO₂, —C(O)—R^(a), —COOR^(a), —C(S)—R^(a), —C(S)OR^(a), —S(O)₂OH, —S(O)₂—R^(a), —S(O)₂NR^(a)R^(b), —O—S(O)—R^(a) and —CON^(a)N^(b); wherein R^(a) and R^(b) are independently selected from the groups consisting of H, alkyl, aryl, arylalkyl-, heteroalkyl, heteroaryl, heteroaryl-alkyl-, or R^(a) and R^(b) together with the atom to which they are attached form a heterocycloalkyl group, and wherein R^(a) and R^(b) may be unsubstituted or further substituted as defined herein.

DETAILED DESCRIPTION

In one aspect, the present invention provides an aqueous platinum electroplating bath comprising:

-   -   a) a source of platinum ions; and     -   b) a source of polyphosphate anions,         and wherein the bath has a pH in the range from about 2 to about         9 when it is in use or ready for use.

The source of platinum ions may be at least one (e.g. 1, 2, 3, 4 or 5 preferably 1) platinum plating salt or complex. The platinum plating salts useful in the invention include a large number of salts or dissolved complexes, for example, diammine dinitroplatinum(II) (i.e. “P Salt”), tetraammineplatinum(II) hydrogen orthophosphate (i.e. “Q Sale”), tetraammineplatinum(II) sulphate, alkali metal hexahydroxyplatinates(IV) (such as sodium hexahydroxyplatinate(IV) or potassium hexahydroxyplatinate(IV)), alkali metal tetranitroplatinates(II) (e.g. sodium tetranitroplatinate(II) or potassium tetranitroplatinate(II)), alkali metal salts of hydrogen hexachloroplatinate(IV) (such as sodium hexachloroplatinate(IV) or potassium hexachloroplatinate(IV)), alkali metal salts of hydrogen dinitrosulphatoplatinate(II) (e.g. sodium dinitrosulphatoplatinate(II) or potassium dinitrosulphatoplatinate(II)), tetraamineplatinum(II) halides (e.g. tetraamineplatinum(II) chloride), alkali metal tetrahaloplatinates(II) (e.g. sodium tetrachloroplatinate(II) or potassium tetrachloroplatinate(II)), tetraamineplatinum(II) hydrogen carbonate, tetraammineplatinum(II) hydroxide and tetraamineplatinum(II) nitrate. The platinum ions may be cationic or anionic. The platinum ions may be may be at an oxidation state of (II) or (IV).

The bath of the present invention comprises a source of polyphosphate anions. In one embodiment, the polyphosphate anion source may be an alkali metal salt, alkaline earth metal salt or ammonium salt of a polyphosphoric acid, or a mixture thereof. Hydrates or anhydrous salts may be used, although the use of anhydrous salts is not essential as the plating bath is aqueous. When the salt is an alkali metal salt, the salt is preferably a lithium, sodium or potassium salt. When the salt is an alkaline earth metal salt, the salt may be a magnesium or calcium salt. Examples of suitable polyphosphate salts include but are not limited to disodium pyrophosphate dibasic, dipotassium dibasic pyrophosphate, tetrasodium pyrophosphate, tetrasodium pyrophosphate decahydrate, tetrapotassium pyrophosphate, potassium tripolyphosphate, sodium hexametaphosphate, potassium hexametaphosphate, lithium hexametaphosphate, lithium hexametaphosphate.6H₂O, potassium pyrophosphate, sodium pyrophosphate or a mixture thereof.

Alternatively or in addition, the polyphosphate ion source may be a polyphosphoric acid, such as pyrophosphoric acid.

The plating baths when made up to be ready for use suitably have a polyphosphate ion concentration of about 0.1 to about 90 g/litre e.g. about 5 to about 80 g/litre. While it possible for the polyphosphate ion concentration to be greater than about 90 g/litre, this is usually undesirable as the polyphosphate may begin to crystallise out of the plating bath at lower temperatures, e.g. room temperature. This may then create handling or processing difficulties with regard to the plating bath. In some embodiments, the polyphosphate ion concentration is about ≧0.1 g/litre. In some embodiments, the polyphosphate ion concentration is about ≧1 g/litre. In some embodiments, the polyphosphate ion concentration is about ≧2.5 g/litre. In some embodiments, the polyphosphate ion concentration is about ≧5 g/litre. In some embodiments, the polyphosphate ion concentration is about ≧10 g/litre. In some embodiments, the polyphosphate ion concentration is about ≧15 g/litre. In some embodiments, the polyphosphate ion concentration is about ≦85 g/litre, in some embodiments about ≦85 g/litre, in some embodiments about ≦80 g/litre, in some embodiments about ≦75 g/litre, in some embodiments about ≦70 g/litre, in some embodiments about ≦65 g/litre, in some embodiments about ≦60 g/litre, in some embodiments about ≦55 g/litre, in some embodiments about ≦50 g/litre, in some embodiments about ≦45 g/litre, in some embodiments about ≦40 g/litre, in some embodiments about ≦35 g/litre, in some embodiments about ≦30 g/litre, in some embodiments about ≦25 g/litre, in some embodiments about ≦20 g/litre. In one preferred embodiment, the polyphosphate ion concentration is about 10 to about 20 g/litre. In the first instance, the polyphosphate ion concentration may be determined from the mass of the components used to make up the bath. However, when the bath is in use, the polyphosphate ion concentration may be assessed using analytical techniques such as titration, gravimetric methods or ion-chromatography.

The platinum plating bath ready for use or in use has a pH in the range from about 2 to about 9. If the pH of the bath is <2, the bath may be very corrosive which may present equipment problems with its use and containment. For example, the equipment needed to analyse the bath (e.g. HPLC internals and column) may be severely affected, or levellers (if used) or other organic additives (if used), such as wetting agents may be destroyed. Moreover, the range of substrates which may be plated would be limited, as well as the materials used in supporting the workpiece. In addition, the present inventors have found that a bath at a pH of <2 is generally inefficient, plates poorly and may have extensive gas formation on the substrate. If the pH is allowed to drift above 9, the plating rate may increase markedly and the bath may become unstable. Platinum powder may also be generated slowly above pH 9, which is disadvantageous. In certain embodiments, the pH is >2, in certain embodiments ≧2.5, in certain embodiments ≧3, in certain embodiments ≧3.5, in certain embodiments ≧4, in certain embodiments ≧4.5, in certain embodiments ≧5, in certain embodiments ≧5.5, in certain embodiments ≧6, in certain embodiments ≧6.5. In certain embodiments, the pH is ≦8.5, preferably <8.5, for example, ≦8, such as about 7. In one preferred embodiment, the pH is from about 7 to less than about 8.5. A bath having a pH of from about 7 to less than about 8.5 may be termed a “neutral” bath and is an example of a non-corrosive plating bath. A neutral bath is advantageous as there is little bubbling at the cathode as most energy is used in plating.

The pH of the plating bath may be adjusted by the addition of suitable acids, bases or a mixture thereof. For example, “Q Salt®” solution is normally supplied for use at about pH 10 to 11 and the addition of acid is required to lower the pH of the solution. Any suitable inorganic acid, organic acid or mixture thereof may be utilised. Examples of suitable organic acids include but are not limited to formic acid, acetic acid and oxalic acid. Examples of suitable inorganic acids include but are not limited to hydrohalic acids (e.g. HCl, HBr or HI), sulfur-containing acids (e.g. sulphuric acid) and phosphorus-containing acids. Phosphorus-containing acids are particularly preferred, such as hypophosphoric acid (H₃PO₂), phosphorous acid (H₃PO₃), ortho-phosphoric acid (H₃PO₄) or pyrophosphoric acid [(HO)₂P(O)OP(O)(OH)₂]. Pyrophosphoric acid is itself a source of polyphosphate anions. The use of phosphorus-containing acids in combination with polyphosphate salts as the polyphosphate ion source is advantageous as a buffered plating bath may be prepared.

Any suitable inorganic base, organic base or mixture may be utilised to increase the pH of the plating bath, if this is required. Examples of suitable inorganic bases include but are not limited to alkali metal polyphosphates, alkaline earth metal polyphosphates, ammonium polyphosphates, alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkali metal phosphates and alkali metal silicates, such as potassium hydroxide, sodium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, potassium carbonate, sodium phosphate, potassium phosphate, sodium silicate, potassium silicate. Examples of suitable organic bases include but are not limited to amines and tetraalkyl ammonium hydroxides, such as ethanolamine or choline hydroxide.

When the polyphosphate anion source is selected from an alkali metal salt, alkaline earth metal salt or ammonium salt of a polyphosphoric acid such as those described above, the polyphosphate ion source itself may act as a base.

The pH will change slowly as the platinum is plated from the bath. The concentration of the platinum can be maintained in the bath by adding fresh plating solution that comprises the platinum ions, polyphosphate anions, acid (if used) and base (if used). Alternatively, each component may be added individually. Desirably, the plating bath is analysed regularly and replenished as necessary in order to maintain the desired concentration of each component. Suitable concentrations for e.g. the platinum ions and/or polyphosphate anions when the bath is in use are generally those provided above and below in respect of when the bath is ready for use.

The platinum ions and the polyphosphate anions may be obtained from different sources. For example, as described above, the platinum ions may be derived from the platinum plating salts and complexes, and the polyphosphate anions may be derived from the salts of polyphosphoric acid.

In another embodiment, the source of platinum ions and the source of polyphosphate anions may be obtained from the same source. In this embodiment, the source for both may be a platinum polyphosphate salt, such as tetraammineplatinum(II) dihydrogen pyrophosphate, di[tetraammineplatinum(II)]pyrophosphate or Na₂[Pt(NH₃)₄][H₂P₂O₇]. Aqueous solutions of these salts may be acidic (in the range of pH 3-4), neutral (e.g. about 7) or alkaline (e.g. about 7-8). With regard to the acidic aqueous solutions further polyphosphate anions may be added to the bath in order to raise the pH before plating, if necessary (the additional polyphosphate anions, therefore, acting as a secondary source of polyphosphate anions). A neutral or alkaline solution, however, may be used directly in plated if desired without further addition of polyphosphate anions.

For certain platinum electroplating applications, the use of sulfur-containing materials may not be desirable. An example where sulfur-containing materials may not be desirable is the platinum plating of materials for aerospace applications, especially turbine blades. Accordingly, plating baths containing materials such as sulfur-containing platinum plating salts or complexes, or sulfur-containing acids may not be optimal for such applications. In one embodiment, therefore, the aqueous platinum plating bath does not comprise a sulfur-containing platinum plating salt or complex. In another embodiment, the aqueous platinum plating bath does not comprise a sulfur-containing acid.

However, the use of sulfur-containing materials may be suitable for the platinum plating of materials other than for aerospace applications.

In other electroplating applications, it may be desirable to avoid the use of halogen-containing materials, particularly chlorine-containing materials, as they may cause sensitization. In this instance, it may be desirable to use a platinum salt or complex which does not comprise halide ions and to select an acid (if used) which is not a hydrohalic acid.

The plating baths when made up to be ready for use suitably have a platinum ion concentration of about 1 to about 40 g/litre e.g. about 1 to about 30 g/litre. Preferred platinum concentrations depend upon the product to be coated and the coating apparatus but are typically about 5 g/litre to about 20 g/litre for most normal operations. In some embodiments, the platinum ion concentration is ≧5 g/litre, for example, ≧7 g/litre. In some embodiments, the platinum ion concentration is ≧10 g/litre, for example, ≧15 g/litre. In some embodiments, the platinum ion concentration is ≦20 g/litre, for example, ≦15 g/litre.

The plating bath of the present invention may be used at temperatures from about room temperature to about 100° C. In certain embodiments, the temperature may be from about 60° C. to about 100° C., in certain embodiments from about 60° C. to about 95° C., in certain embodiments from about 70° C. to about 95° C., in certain embodiments from about 75° C. to about 95° C., in certain embodiments from about 75° C. to about 90° C., in certain embodiments from about 70° C. to about 90° C. In general, it has been found that the higher the plating temperature, the greater the plating rate. Greater loss of water by evaporation at higher temperatures may occur, however, this may be monitored and adjusted as appropriate through the addition of water to the bath.

The bath of the invention may be used successfully under broadly conventional conditions and current densities. For example, the current density may be from about 2 to about 10 mA/cm², for example, from about 2 to about 6 mA/cm², such as about 4 mA/cm² The bath can be used to plate using complex methods such as pulse plating or impressed AC ripple or other interrupted plating techniques, but direct current electroplating is preferred.

The aqueous platinum electroplating bath is suitable for use in an industrial or commercial electroplating process. The bath of the present invention may be used to rapidly coat large substrates in an industrial sized tank in a continual process rather than being restricted to a research tool explored by cyclic voltammetry, or by other electrochemical probing techniques in a small cell, whilst confined to a small cell. Accordingly, the rate at which the platinum is plated out of solution should be such that the process is commercially viable. In one embodiment, therefore, the rate of plating is about ≧0.5 microns thickness of platinum per hour. In yet another embodiment, the rate of plating is about ≧1 micron thickness of platinum per hour. In another embodiment, the rate of plating is about ≧1.5 microns thickness of platinum per hour. In yet another embodiment, the rate of plating is about ≧2 microns thickness of platinum per hour. In another embodiment, the rate of plating is about ≧2.5 microns thickness of platinum per hour. In yet another embodiment, the rate of plating is about ≧3 microns thickness of platinum per hour. In another embodiment, the rate of plating is about ≧3.5 microns thickness of platinum per hour. In yet another embodiment, the rate of plating is about ≧4 microns thickness of platinum per hour. In another embodiment, the rate of plating is about ≧4.5 microns thickness of platinum per hour. In yet another embodiment, the rate of plating is about ≧5 microns thickness of platinum per hour. In another embodiment, the rate of plating is about ≧5.5 microns thickness of platinum per hour. In yet another embodiment, the rate of plating is about ≧6 microns thickness of platinum per hour. In another embodiment, the rate of plating is about ≧6.5 microns thickness of platinum per hour. In yet another embodiment, the rate of plating is about ≧7 microns thickness of platinum per hour. In another embodiment, the rate of plating is about ≧7.5 microns thickness of platinum per hour. In yet another embodiment, the rate of plating is about ≧8 microns thickness of platinum per hour. In another embodiment, the rate of plating is about ≧8.5 microns thickness of platinum per hour. In yet another embodiment, the rate of plating is about ≧9 microns thickness of platinum per hour. In another embodiment, the rate of plating is about ≧9.5 microns thickness of platinum per hour. In another embodiment, the rate of plating is about ≧10 microns thickness of platinum per hour. In one preferred embodiment, the rate of plating is from about 5 microns thickness of platinum per hour to about 10 microns thickness per hour. When the plating bath comprises one or more other plating salts or complexes (which are not platinum plating salts or complexes), the above embodiments relate to the plating rate and thickness of platinum alloy per hour.

Deposition of platinum onto shaped parts may give an uneven thickness of platinum in some electroplating systems. While this can be alleviated by the use of a shaped anode to modify the electric field around the part and thereby moderate the extremes of field which cause uneven distribution, it is nevertheless desirable to find an alternative way of producing an even deposit. The platinum electroplating bath of the present invention therefore may further comprise at least one leveller. In certain embodiments, the leveller may contribute to the production of a bright or shiny plate. In certain embodiments, the leveller may contribute to the lustre of the produced plate. In certain embodiments, the leveller may help to generate a plate with increased hardness.

In one embodiment, the leveller comprises at least one unsaturated carbon-carbon or unsaturated carbon-heteroatom bond.

Preferably, the leveller is selected from the group consisting of at least one:

a) substituted or unsubstituted saccharine or salt thereof; b) substituted or unsubstituted benzopyranone; c) substituted or unsubstituted benzaldehyde or derivative thereof; d) substituted or unsubstituted alkene provided the alkene is not ethylene; e) substituted or unsubstituted alkyne provided the alkyne is not acetylene; f) substituted or unsubstituted alkylnitrile; g) substituted or unsubstituted pyridine or addition salt thereof; h) substituted or unsubstituted triazole; and i) substituted or unsubstituted pyridinium salt.

The leveller may be a substituted or unsubstituted saccharine or salt thereof. In one preferred embodiment, therefore, the leveller is a compound of formula (1) or salts thereof:

wherein m is 0, 1, 2, 3 or 4; each R₁ is independently an unsubstituted C₁-C₁₀ alkyl group; R₂ is selected from the group consisting of H, unsubstituted C₁-C₁₀ alkyl, an alkali metal ion and an alkaline earth metal ion.

In one preferred embodiment, m is 0 i.e. the aryl group is unsubstituted. In another preferred embodiment, R₂ is H. In yet another preferred embodiment, the compound of formula (1) is a salt wherein R₂ is an alkali metal cation or an alkaline earth metal cation e.g. Na⁺, K⁺ or Ca²⁺. Examples of compounds of formula (1) include but are not limited to saccharine, sodium saccharine, potassium saccharine and calcium saccharine.

When the compound of formula (1) is a salt, the anionic sulfobenzimide group may be present as an amido tautomer (for example see the structure of calcium saccharine above) and/or as the iminyl tautomer (for example see the structure of sodium and potassium saccharine above). The amido and iminyl tautomers are included within the definition of the compound of formula (1).

When the leveller is a substituted or unsubstituted benzopyranone, the benzopyranone may be a substituted or unsubstituted 1-benzopyran-2-one, 2-benzopyran-1-one or 1-benzopyran-4-one. In one preferred embodiment, the leveller is a compound of formula (2a), (2b) or (2c):

wherein n is 0, 1, 2, 3 or 4; p is 0, 1 or 2; each R₁₀ and R₁₁ is independently selected from an unsubstituted C₁-C₁₀ alkyl group.

In one embodiment, the leveller is a compound of formula (2a). In another embodiment, the leveller is a compound of formula (2b). In yet another embodiment, the leveller is a compound of formula (2c).

In one preferred embodiment, n is 0 i.e. the aryl group is unsubstituted. In another preferred embodiment, p is 0. An example of a compound of formula (2a) includes but is not limited to coumarin.

The leveller may be a substituted or unsubstituted benzaldehyde or derivative thereof. In one preferred embodiment, the leveller is a compound of formula (3a) or (3b):

wherein R₂₀ is selected from the group consisting of H and —OR₂₃; and R₂₁ and R₂₂ are independently selected from the group consisting of H, —C(O)R₂₄ and unsubstituted C₁-C₁₀-alkyl; and R₂₃ and R₂₄ are independently selected from the group consisting of H and unsubstituted C₁-C₁₀-alkyl.

In one embodiment, the leveller is a compound of formula (3a). In another embodiment, the leveller is a compound of formula (3b).

Preferably, R₂₀ is selected from the group consisting of H, —OH, —OMe, —OEt, —OPr (n- or i-) and —OBu (n-, i- or t-) and more preferably, H, —OH and —OMe. In this instance, therefore, R₂₃ is preferably —H, -Me, -Et, -Pr (n- or i-), -Bu (n-, i- or t-) and more preferably —H or —OMe.

Preferably, each R₂₁ and R₂₂ is independently selected from the group consisting of H, methyl, ethyl, propyl (n- or i-), butyl (n-, i- or t-), —C(O)H, —COMe, —COEt, —COPr (n- or i-) and —COBu (n-, i- or t-). More preferably, each R₂₁ and R₂₂ is independently selected from the group consisting of H, methyl, ethyl and —COMe. In these cases, R₂₄ is preferably H, methyl, ethyl, propyl (n- or i-), butyl (n-, i- or t-) and more preferably Me.

Examples of compounds of formula (3a) include but are not limited to vanillin, ethyl vanillin, vanillin acetate, vanillic acid and methyl vallinate. Examples of compounds of formula (3b) include but are not limited to ortho-vanillin and 3-methoxysalicylic acid.

The leveller may be a substituted or unsubstituted alkene. In this instance, it is preferred that the leveller is not ethylene. In one preferred embodiment, the leveller is a compound of formula (4):

wherein each R₃₀, R₃₁, R₃₂ and R₃₃ is independently selected from the group consisting of H, unsubstituted C₁-C₁₀-alkyl, substituted C₁-C₁₀-alkyl, —CO₂R₃₄, —NR₃₄R₃₅, —CONR₃₄R₃₅ and —CN, provided that R₃₀, R₃₁, R₃₂ and R₃₃ are not all H, wherein the substituents are selected from the group consisting of at least one (e.g. 1, 2, 3, 4 or 5)—OH, —CO₂R₃₆, —OC(O)R₃₆, —NR₃₆R₃₇, —CONR₃₆R₃₇, —SO₃ ⁻Na⁺ and —SO₃ ⁻K⁺; R₃₄ and R₃₅ are independently selected from the group consisting of H and unsubstituted C₁-C₁₀-alkyl; and R₃₆ and R₃₇ are independently selected from the group consisting of H and unsubstituted C₁-C₁₀-alkyl.

The compounds of formula (4) may be cis-, trans- or geminal-alkenyl compounds. When the compound of formula (4) is cis-, R₃₀ and R₃₂ or R₃₁ and R₃₃ are H. When the compound of formula (4) is trans-, R₃₀ and R₃₃ or R₃₁ and R₃₂ are H. When the compound of formula (4) is geminal-, R₃₀ and R₃₁ or R₃₂ and R₃₃ are H. Alternatively, R₃₀, R₃₁, R₃₂ and R₃₃ may each be substituted with a group other than H.

Preferably, each R₃₀, R₃₁, R₃₂ and R₃₃ is independently selected from the group consisting of H, unsubstituted C₁-C₁₀-alkyl, substituted C₁-C₁₀-alkyl, —NH₂ and —CN. Preferably, the substituents are selected from the group consisting of at least one (e.g. 1, 2, 3, 4 or 5) —OH, —OC(O)Me, —NH₂, —CN and —SO₃ ⁻Na⁺ and —SO₃ ⁻K⁺. More preferably, each R₃₀, R₃₁, R₃₂ and R₃₃ is independently selected from the group consisting of H, —CH₂—OH, —CH(OH)CH₂—OH, —NH₂ and —CN. Examples of compounds of formula (4) include but are not limited to butenediol (e.g. trans-1,4-butenediol, cis-2-butene-1,4-diol, or 3-butene-1,2-diol) and diaminomaleonitrile.

The leveller may be a water-soluble substituted or unsubstituted C₂-C₁₀-alkyne provided the alkyne is not acetylene. In a preferred embodiment, the leveller is a compound of formula (5):

wherein R₄₀ and R₄₁ are independently selected from the group consisting of H, unsubstituted C₁-C₁₀-alkyl and substituted C₁-C₁₀-alkyl, provided that R₄₀ and R₄₁ are not both H, wherein the substituents are selected from the group consisting of at least one (e.g. 1, 2, 3, 4 or 5) of —OH, —CO₂R₄₂, —OC(O)R₄₂, —NR₄₂R₄₃, —CONR₄₂R₄₃, —CN, —SO₃ ⁻Na⁺ and −SO₃ ⁻K⁺; R₄₂ and R₄₃ are independently selected from the group consisting of H and unsubstituted C₁-C₁₀-alkyl.

Preferably, R₄₀ and R₄₁ are independently selected from the group consisting of H, unsubstituted C₁-C₁₀-alkyl and substituted C₁-C₁₀-alkyl, wherein the substituents are selected from the group consisting of at least one (e.g. 1, 2, 3, 4 or 5) of —OH, OC(O)Me, —NH₂, —CN, —SO₃ ⁻Na⁺ and —SO₃ ⁻K⁺. More preferably, R₄₀ and R₄₁ are independently selected from the group consisting of H, —CH₂—OH, —CH(OH)CH₂—OH and —CH₂OC(O)Me. Examples of compounds of formula (5) include but are not limited to 1,4-butynediol, 1,4-butynediol diacetate and propargyl alcohol.

When the leveller is a substituted or unsubstituted alkylnitrile, it is preferred that the leveller is a compound of formula (6):

R₅₀—CN  (6)

wherein R₅₀ is a substituted or unsubstituted C₁-C₁₀-alkyl, and the substituents are selected from the group consisting of at least one (e.g. 1, 2, 3, 4 or 5) of −OR₅₁, —CO₂R₅₁, —OC(O)R₅₁, —NR₅₁R₅₂ and —CN; and wherein R₅₁ and R₅₂ are independently selected from the group consisting of H and unsubstituted C₁-C₁₀-alkyl.

Preferably, R₅₀ is a substituted or unsubstituted C₁-C₁₀-alkyl, wherein the substituents are selected from the group consisting of at least one (e.g. 1, 2, 3, 4 or 5) of —OH, —OMe, —OPr (n- or i-), —OBu (n-, or t-), —CO₂H, —NH₂ and —CN. More preferably, R₅₀ is selected from the group consisting of —CH₂CH₂—OH, —CH(OH)—CH₃, —CH₂CO₂H and —CH₂—CH₂—CN. Examples of compounds of formula (6) include but are not limited to 3-hydroxypropionitrile, 2-hydroxypropionitrile, cyanoacetic acid and succinonitrile

In another embodiment, the leveller may be a substituted or unsubstituted pyridine or an addition salt thereof. Preferably, the leveller is a compound of formula (7a), (7b) or (7c):

wherein R₆₀ and R₆₁ are independently selected from the group consisting of —OH, —CN, —CONR₆₂R₆₃, —CO₂R₆₂, —COR₆₃, N-(unsubstituted C₁-C₁₀-alkyl)-pyrrolidinyl, unsubstituted C₁-C₁₀-alkyl, substituted C₁-C₁₀-alkyl, unsubstituted C₂-C₁₀-alkenyl, substituted C₂-C₁₀-alkenyl, —SO₂—R₆₃, —N═N-(unsubstituted C₆-C₁₀-aryl), —N═N-(substituted C₆-C₂₀-aryl), unsubstituted pyridyl, substituted pyridyl, wherein the substituents are independently selected from the group consisting of at least one (e.g. 1, 2, 3, 4 or 5) of —CN, —CONR₆₄R₆₅, —COR₆₅, —CO₂R₆₄, —OH, —NR₆₄R₆₅ and ═NR₆₄; R₆₂ is selected from the group consisting of H, —OH and unsubstituted C₁-C₁₀-alkyl; R₆₃ is selected from the group consisting of H, —OH, unsubstituted C₁-C₁₀-alkyl, unsubstituted C₁-C₁₀-alkyl-CO₂H, —NH₂, —NH(unsubstituted C₁-C₁₀-alkyl), —N(unsubstituted C₁-C₁₀-alkyl)₂; R₆₄ is selected from the groups defined for R₆₂; R₆₅ is selected from the groups defined for R₆₃; each x is 0, 1, 2 or 3; and each y is 0, 1, 2, 3 or 4.

In one embodiment, the leveller is a compound of formula (7a). In another embodiment, the leveller is a compound of (7b). In yet another embodiment, the leveller is a compound of (7c).

In one embodiment, the compound of formula (7a) is unsubstituted i.e. x is 0. In another embodiment, x is 1 i.e. the compound (7a) is monosubstituted. In this instance, the substituent R₆₀ may be attached to any one of the carbons in the pyridine ring i.e. at C-2, C-3 or C-4. In another embodiment, x is 2 for the compound of (7a) i.e. the compound is disubstituted. In this instance, each substituent R₆₀ may be the same or different. The substituents may be attached to any of the carbons in the pyridine ring i.e. the compound (7a) may be 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5- or 3,6-disubstituted. In another embodiment, compound (7a) is trisubstituted i.e x is 3. In this instance, each substituent R₆₀ may be the same or different. The substituents may be attached to any of the carbons in the pyridine ring i.e. the compound (7a) may be 2,3,4-, 2,3,5-, 2,3,6-, 2,4,5-, 2,4,6-, 3,4,5- or 3,4,6-trisubstituted.

In one embodiment, x may be 0, 1, 2 or 3 for the compound of formula (7b). When x is 0, the pyridinyl ring is unsubstituted. In another embodiment, when x is 1, the R₆₀ substituent may be attached at any of the carbon atoms at C-2, C-3 or C-4. In yet another embodiment, when x is 2, each R₆₀ substituent may be the same or different. The substituents may be attached to any of the carbons in the pyridine ring i.e. the compound (7b) may be 2,3-, 2,4- or 3,4-substituted. In another embodiment, x is 3 and each R₆₀ is attached at C-2, C-3 and C-4. In this instance, each substituent R₆₀ may be the same or different.

In another embodiment, y may be 0, 1, 2, 3 or 4 for the compound (7b). In one embodiment, y is 0. In yet another embodiment, y is 1. In this instance, the substituent R₆₁ may be attached to any of the carbon atoms at C-5, C-6, C-7 or C-8. In yet another embodiment, when y is 2, each R₆₁ substituent may be the same or different. The substituents may be attached in any substitution pattern to any of the carbons at C-5, C-6, C-7 or C-8 i.e. the compound (7b) may be 5,6-, 5,7-, 5,8-, 6,7-, 6,8- or 7,8-substituted. In another embodiment, when y is 3, each R₆₁ substituent may be the same or different. The substituents may be attached in any combination to the carbons at C-5, C-6, C-7 or C-8 i.e. the compound (7b) may be 5,6,7-, 5,6,8-, 5,7,8- or 6,7,8-substituted. In another embodiment, y is 4 and each R₆₁ is attached at C-5, C-6, C-7 and C-8. In this instance, each substituent R₆₁ may be the same or different.

In one embodiment, x and y are 0 i.e. compound (7b) is quinoline.

In one embodiment, x may be 0, 1, 2 or 3 for the compound of formula (7c). When x is 0, the pyridinyl ring is unsubstituted. In another embodiment, when x is 1, the R₆₀ substituent may be attached at any of the carbon atoms at C-1, C-3 or C-4. In yet another embodiment, when x is 2, each R₆₀ substituent may be the same or different. The substituents may be attached to any of the carbons in the pyridine ring i.e. the compound (7c) may be 1,3-, 1,4- or 3,4-substituted. In another embodiment, x is 3 and each R₆₀ is attached at C-1, C-3 and C-4. In this instance, each substituent R₆₀ may be the same or different.

In another embodiment, y may be 0, 1, 2, 3 or 4 for the compound (7c). In one embodiment, y is 0. In yet another embodiment, y is 1. In this instance, the substituent R₆₁ may be attached to any of the carbon atoms at C-5, C-6, C-7 or C-8. In yet another embodiment, when y is 2, each R₆₁ substituent may be the same or different. The substituents may be attached in any combination to any of the carbons at C-5, C-6, C-7 or C-8 i.e. the compound (7c) may be 5,6-, 5,7-, 5,8-, 6,7-, 6,8- or 7,8-substituted. In another embodiment, when y is 3, each R₆₁ substituent may be the same or different. The substituents may be attached in any combination to the carbons at C-5, C-6, C-7 or C-8 i.e. the compound (7c) may be 5,6,7-, 5,6,8-, 5,7,8- or 6,7,8-substituted. In another embodiment, y is 4 and each R₆₁ is attached at C-5, C-6, C-7 and C-8. In this instance, each substituent R₆₁ may be the same or different.

In one embodiment, x and y is 0 i.e. compound (7c) is isoquinoline.

Preferably, R₆₀ is selected from the group consisting of —OH, —CN, —CONR₆₂R₆₃, —CO₂R₆₂, —COR₆₃, N-(unsubstituted C₁-C₁₀-alkyl)-pyrrolidinyl, unsubstituted C₁-C₁₀-alkyl, substituted C₂-C₁₀-alkenyl, —SO₂—R₆₃, —N═N-(substituted C₆-C₂₀-aryl) and unsubstituted pyridyl. Preferably, the substituents are selected from the group consisting of at least one (e.g. 1, 2, 3, 4 or 5) —CN, —CONH₂, —CONHMe, —CONHEt, —CONMe₂, —CONEt₂, —COH, —CO₂H, —CO₂Me, —CO₂Et, —OH, —NH₂, ═N—OH, —NMe₂, —NEt₂, —NMeEt. R₆₂ and R₆₄ are preferably independently selected from the group consisting of H, —OH, methyl, ethyl, propyl (n- or i-) and butyl (n-, i- or t-). R₆₃ and R₆₅ are preferably independently selected from the group consisting of H, —OH, methyl, ethyl, propyl (n- or i-), butyl (n-, i- or t-), —NH₂, —NHMe, —NHEt, —NHPr (n- or i-), —NHBu (n-, i- or t-), —NMe₂, —NEt₂, —NPr₂ (wherein each Pr group is independently n- or i-), —NBu₂ (wherein each Bu group is independently n-, i- or t-) and —CH₂—CO₂H. In one preferred embodiment, R₆₀ is selected from the group consisting of methyl, ethyl, propyl (n- or i-), butyl (n-, i- or t-), —CN, —CO₂H, —COH, —CONH(OH), —CONH(NH₂), —CONH₂, N-Me-pyrrolidinyl-2-yl, —CO₂Me, —CONMe₂, —CO₂Et, —CONEt₂, —CONMeEt, —C═C—CO₂H, —SO₂OH, —N═N-(2,4-dihydroxy-phenyl), -pyridyl, —C(NOH)(NH₂), —C(NOH)(NMe₂), —C(NOH)(NEt₂), —C(NOH)(NMeEt) and —CONH(CH₂CO₂H). In one preferred embodiment, R₆₁ is selected from the group consisting of methyl, ethyl, propyl (n- or i-), butyl (n-, i- or t-), —CN, —CO₂H, —COH, —CONH(OH), —CONH(NH₂), —CONH₂, N-Me-pyrrolidinyl-2-yl, —CO₂Me, —CONMe₂, —CO₂Et, —CONEt₂, —CONMeEt, —C═C—CO₂H, —SO₂OH, —N═N-(2,4-dihydroxy-phenyl), -pyridyl, —C(NOH)(NH₂), —C(NOH)(NMe₂), —C(NOH)(NEt₂), —C(NOH)(NMeEt) and —CONH(CH₂CO₂H). In another preferred embodiment, R₆₁ is selected from the group consisting of methyl, ethyl, propyl (n- or i-), butyl (n-, i- or t-), —CN, —CO₂H, —COH, —CONH(OH), —CONH(NH₂), —CONH₂, —CO₂Me, —CONMe₂, —CO₂Et, —CONEt₂, —CONMeEt, —C(NOH)(NH₂), —C(NOH)(NMe₂), —C(NOH)(NEt₂), and —C(NOH)(NMeEt).

Examples of compounds of formula (7a), (7b) and (7c) include but are not limited to 4-cyanopyridine, 2-cyanopyridine, nicotinic hydrazide, iso-nicotinamide, nicotinamide, iso-nicotinic acid, nicotinic acid, nicotine, methyl nicotinate, N,N-dimethylnicotinamide, trans-3-(3-pyridyl)acrylic acid, trans-3-(4-pyridyl)acrylic acid, pyridine-3-sulfonic acid, 4-(2-pyridylazo)resorcinol, iso-nicotinaldehyde, nicotinaldehyde, bipyridyl (2,2′- and 4,4′-), quinoline, isoquinoline or other compound of formula (7a), (7b) or (7c) illustrated below.

It is possible for a compound of formula (7) to convert to another compound of formula (7) under the conditions used in the plating bath of the present invention, i.e such as one compound of formula (7a) to another compound of formula (7a), a compound (7b) to another compound (7b) or a compound (7c) to another compound (7c). For example, 4-cyanopyridine, iso-nicotinamide and iso-nicotinaldehyde may each convert to iso-nicotinic acid, whereas 3-cyanopyridine, nicotinamide, nicotinaldehyde and nicotinic hydrazide may each convert to nicotinic acid. The compound of formula (7) therefore includes within its scope the starting compound of formula (7), the converted compound of formula (7) and mixtures thereof. In this embodiment, it is not envisaged that e.g. a compound (7a) would convert to e.g. a compound (7c) or vice versa.

When the compound of formula (7a), (7b) or (7c) is an addition salt, the salt may be an alkali metal salt, an alkaline earth metal salt or an ammonium salt. In one preferred embodiment, the salt is a sodium, potassium, calcium or ammonium salt. Examples of salts of compound of formula (7a), (7b) or (7c) include but are not limited to nicotinic acid sodium salt, nicotinic acid potassium salt, nicotinic acid calcium salt, nicotinic acid ammonium salt, iso-nicotinic acid sodium salt, iso-nicotinic acid potassium salt, iso-nicotinic acid calcium salt and iso-nicotinic acid ammonium salt.

When the leveller is a substituted or unsubstituted triazole, the triazole may be a 1,2,3- or a 1,2,4-triazole. In one embodiment, the leveller is a compound of formula (8):

wherein R₇₀ is selected from a group consisting of H, —CO₂R₇₂ and —NR₇₂R₇₃; R₇₁ is selected from a group consisting of H and unsubstituted C₁-C₁₀-alkyl; R₇₂ and R₇₃ are independently selected from the group consisting of H and unsubstituted C₁-C₁₀-alkyl; one of X₁ and X₂ is C—R₇₄ and the other of X₁ and X₂ is N; and R₇₄ is selected from a group as defined for R₇₀.

In one embodiment, X₁ is C—R₇₄ and X₂ is N. In another embodiment, X₂ is C—R₇₄ and X₁ is N.

Preferably, R₇₀ is selected from a group consisting of H, —CO₂H, —CO₂Me, —CO₂Et, —CO₂Pr (n- or i-), —CO₂Bu (n-, i- or t-), —NH₂, —NHMe, —NHEt, —NHPr (n- or i-), —NHBu (n-, i- or t-), —NMe₂, —NEt₂, —NPr₂ (wherein each Pr group is independently n- or i-) and —NBu₂ (wherein each Bu group is independently n-, i- or t-). R₇₂ and R₇₃ therefore are independently selected from the group consisting of H, methyl, ethyl, propyl (n- or i-) and butyl (n-, i- or t-). R₇₁ is preferably selected from a group consisting of H, methyl, ethyl, propyl (n- or i-) and butyl (n-, i- or t-). R₇₄ is preferably selected from the group consisting of H, —CO₂H, —CO₂Me, —CO₂Et, —CO₂Pr (n- or i-), —CO₂Bu (n-, i- or t-), —NH₂, —NHMe, —NHEt, —NHPr (n- or i-), —NHBu (n-, i- or t-), —NMe₂, —NEt₂, —NPr₂ (wherein each Pr group is independently n- or i-) and —NBu₂ (wherein each Bu group is independently n-, i- or t-). Examples of compounds of formula (8) include but are not limited to 3-amino-1,2,4-triazole and 3-amino-1,2,4-triazole-5-carboxylic acid.

The leveller may be a substituted or unsubstituted pyridinium salt. Preferably, the leveller is a compound of formula (9a), (9b) or (9c):

wherein R₆₀ and R₆₁ are independently selected from the group consisting of —OH, —CN, —CONR₆₂R₆₃, —CO₂R₆₂, —COR₆₃, N-(unsubstituted C₁-C₁₀-alkyl)-pyrrolidinyl, unsubstituted C₁-C₁₀-alkyl, substituted C₁-C₁₀-alkyl, unsubstituted C₂-C₁₀-alkenyl, substituted C₂-C₁₀-alkenyl, —SO₂—R₆₃, —N═N-(unsubstituted C₆-C₁₀-aryl), —N═N-(substituted C₆-C₂₀-aryl), unsubstituted pyridyl, substituted pyridyl, wherein the substituents are independently selected from the group consisting of at least one (e.g. 1, 2, 3, 4 or 5) of —CN, —CONR₆₄R₆₅, —COR₆₅, —CO₂R₆₄, —OH, —NR₆₄R₆₅ and ═NR₆₄; R₆₂ is selected from the group consisting of H, —OH and unsubstituted C₁-C₁₀-alkyl; R₆₃ is selected from the group consisting of H, —OH, unsubstituted C₁-C₁₀-alkyl, unsubstituted C₁-C₁₀-alkyl-CO₂H, —NH₂, —NH(unsubstituted C₁-C₁₀-alkyl), —N(unsubstituted C₁-C₁₀-alkyl)₂; R₆₄ is selected from the groups defined for R₆₂; R₆₅ is selected from the groups defined for R₆₃; R₈₂ is selected from the group consisting of —O⁻ and unsubstituted C₁-C₁₀-alkyl; Z is a counterion when R₈₂ is an unsubstituted C₁-C₁₀-alkyl; each x is 0, 1, 2 or 3; and each y is 0, 1, 2, 3 or 4.

In one embodiment, the leveller is a compound of formula (9a). In another embodiment, the leveller is a compound of formula (9b). In yet another embodiment, the leveller is a compound of formula (9c).

The various embodiments for R₆₀, R₆₁, R₆₂, R₆₃, R₆₄, R₆₅, x and y are as generally described above with regard to the compounds of formulae (7a), (7b) and (7c) and each of these embodiments can be considered recited herein with regard to the compounds of formulae (9a), (9b) and (9c).

R₈₂ is a substituent attached to the nitrogen atom. In one embodiment, R₈₂ may be —O⁻ i.e. the compound of formula (9a), (9b) or (9c) is an N-oxide. In this instance, a counterion Z is generally not required in order to stabilise the pyridinyl N atom. In another embodiment, R₈₂ may be an unsubstituted C₁-C₁₀-alkyl, such as methyl, ethyl, propyl (n- or i-), butyl (n-, i- or t-). In this embodiment, a counterion Z is required and any suitable counterion may be utilised, for example, halide anions such as F, Cl⁻, Br or I⁻.

It is possible for a compound of formula (9) to convert to another compound of formula (9) under the conditions used in the plating bath of the present invention, i.e such as one compound of formula (9a) to another compound of formula (9a), a compound (9b) to another compound (9b) or a compound (9c) to another compound (9c). The compound of formula (9) therefore includes within its scope the starting compound of formula (9), the converted compound of formula (9) and mixtures thereof. In this embodiment, it is not envisaged that e.g. a compound (9a) would convert to e.g. a compound (9c) or vice versa.

Examples of compounds of formula (9a), (9b) and (9c) include but are not limited to those illustrated below:

Alternatively, the leveller may be a substituted or unsubstituted polyalkyleneimine. In this instance, the leveller is preferably unsubstituted polyethyleneimine or ethoxylated polyethyleneimine.

Before the bath is utilised in a plating process, the leveller may in insoluble, partially soluble or substantially completely soluble in the other bath components. However, when the bath is in use it is desirable that the leveller is substantially completely soluble at the desired plating temperature.

The leveller may be added in any suitable quantity, for example, from about 0.0001 g/litre to about 10 g/litre. In one embodiment, the concentration of leveller is about ≧0.001 g/litre, in another embodiment about ≧0.01 g/litre, in another embodiment about ≧03.1 g/litre. In another embodiment, the concentration of leveller is about ≦9 g/litre, in another embodiment about ≦8 g/litre, in another embodiment about ≦7 g/litre, in another embodiment about ≦6 g/litre, in another embodiment about ≦5 g/litre. In yet another embodiment, the concentration of the leveller is about 0.01 g/litre to about 5 g/litre.

In one embodiment, the aqueous platinum electroplating bath may comprise more than one leveller e.g. 2, 3, 4, or 5 levellers. In this instance, each leveller may be independently selected from those as described above.

If desired, the plating bath of the present invention may comprise one or more other plating salts or complexes, such as platinum group metal (PGM) plating salts or complexes, or base metal plating salts or complexes. The PGM salts or complexes may be rhodium, palladium, iridium, ruthenium or rhenium plating salts or complexes, such as HReO₄. Base metal plating salts include but are not limited to hexaamminenickel(II) chloride.

The bath may be prepared by adding the components in any suitable order, for example, in one method an acid (if used) may be added to an aqueous solution of the platinum ions, followed by the polyphosphate anion source, base (if used), leveller (if used) and other components (if used). In another method, a base may be added to an aqueous solution of a platinum polyphosphate salt, followed by a leveller (if used) and other components (if used).

Depending on the substrate to be plated, the plating baths may further comprise one or more brighteners or other components, for example, surfactants or wetting agents to suppress bubble formation on the substrate. Suitable wetting agents/surfactants include polyethyleneglycol 50% aqueous solution or long chain alkyl sarcosines.

In another aspect, the invention includes a method of plating a PGM onto a substrate, comprising electroplating using the bath of the invention. The substrate is preferably a conductive substrate, such as a metal, conductive plastic or conductive ceramic.

In yet another aspect, the invention includes a platinum salt which is tetraammineplatinum(II) dihydrogen pyrophosphate, di[tetraammineplatinum(II)]pyrophosphate or Na₂[Pt(NH₃)₄][H₂P₂O₇]. In one embodiment, the platinum plating salt is tetraammineplatinum(II) dihydrogen pyrophosphate. In another embodiment, the platinum plating salt is di[tetraammineplatinum(II)]pyrophosphate. In another embodiment, the platinum plating salt is Na₂[Pt(NH₃)₄][H₂P₂O₇].

In another aspect, the invention includes the use of an aqueous platinum plating bath as defined herein for plating platinum or platinum alloy onto a substrate. In one embodiment, platinum is plated onto a substrate. In another embodiment, a platinum alloy is plated onto a substrate. The substrate may be a metal (e.g. a metal article or metal powder), conductive plastic or conductive ceramic (such as a zirconia oxygen sensor or ceramic ozone destructor for motor vehicles or aircraft).

In yet another aspect, the invention includes a method for the preparation of tetraammineplatinum(II) dihydrogen pyrophosphate comprising the step of reacting Pt(NH₃)₄(OH)₂ or Pt(NH₃)₄(HCO₃)₂ with pyrophosphoric acid in water, wherein the molar ratio of Pt(NH₃)₄(OH)₂ or Pt(NH₃)₄(HCO₃)₂: pyrophosphoric acid is about 1: about 1.

In another aspect, the invention includes a method for the preparation of di[tetraammineplatinum(II)]pyrophosphate comprising the step of reacting Pt(NH₃)₄(OH)₂ or Pt(NH₃)₄(HCO₃)₂ with pyrophosphoric acid in water, wherein the molar ratio of Pt(NH₃)₄(OH)₂ or Pt(NH₃)₄(HCO₃)₂: pyrophosphoric acid is about 1: about 0.5.

In another aspect, the invention includes a method for the preparation of Na₂[Pt(NH₃)₄][H₂P₂O₇] comprising the step of reacting Pt(NH₃)₄(OH)₂ or Pt(NH₃)₄(HCO₃)₂ with Na₂H₂P₂O₇ in water, wherein the molar ratio of Pt(NH₃)₄(OH)₂ or Pt(NH₃)₄(HCO₃)₂: Na₂H₂P₂O₇ is about 1:about 1.

If desired tetraammineplatinum(II) dihydrogen pyrophosphate, di[tetraammineplatinum(II)]pyrophosphate and Na₂[Pt(NH₃)₄][H₂P₂O₇] may be used as aqueous solutions. Alternatively, the platinum complexes may be isolated as solids using known methods.

The invention will now be described by way of the following non-limiting Examples and with reference to the following Figures in which:

FIG. 1 illustrates a shaped part of the given dimensions which is used to assess the deposition of platinum (or platinum alloys) onto shaped parts.

FIG. 2 is a distribution plot of platinum thickness at locations 1-8 identified in FIG. 1.

EXAMPLES General

20Q “Q Salt®” material is commercially available from Johnson Matthey and is an ammoniacal solution of tetraammineplatinum(II) hydrogen phosphate at a pH of about 10 to 11 and 20 g/l Pt.

Unless otherwise stated, substrates were 9×2.5 cm panels, thickness 1 mm for 316 stainless steel and 2 mm for brass. The brass panels were either manually polished using “Brasso®” or grit blasted using Type 150 and 180/220 brown aerospace grade grit; stainless steel panels were cleaned and degreased using 1M sodium hydroxide solution, followed by a dip in 6M hydrochloric acid.

The shaped substrates as shown in FIG. 1 were of Iconel or 316 stainless steel and were treated before use by grit blasting with 180/220 brown aerospace grit and alkali cleaning using 1M sodium hydroxide solution for 6 minutes at a temperature of at least 60° C., followed by a dip (1-2 minutes) in 6M hydrochloric acid at room temperature. The substrates were washed thoroughly between each treatment.

The panels were immersed in the plating baths to a depth of 5 cm, within 150, 400 or 600 ml glass beakers. The anode and cathode were 4 cm apart if a 400 ml beaker was used and 2.5 cm apart if a 150 ml beaker was used. The substrates were used as cathodes and the anode was a platinised titanium sheet (plated on both sides) placed directly opposite the cathode or a circular platinised titanium mesh surrounding the cathode. The circular platinised titanium mesh was placed around the inner circumference wall of the glass beaker.

Example 1

45% phosphoric acid was added dropwise with stirring to 50 ml of 20Q tetraammineplatinum(II) hydrogen phosphate solution until the pH was about 3. 4.5 g tetrasodium pyrophosphate.10H₂O was then dissolved in the solution, and made up to 120 ml with water. The solution had a pH of 7. 7 ml of 1M sodium hydroxide solution was added to give a bath of pH 8. The initial concentration of Pt as metal in the bath was approx. 8.3 g/l.

The bath was used to plate platinum onto a substrate of gritted steel under the conditions: 1.80 V, 075 mA, 80-85° C., plate time 1 hour at approximately pH=8 with the pH slightly falling by 0.5 during the deposition. An attractive bright coating was obtained of weight 0.3016 g platinum.

Example 2

A plating bath was made up from 50 ml of 20Q tetraammineplatinum(II) hydrogen phosphate solution at pH 10-11, to which was added 3 g of tetrasodium pyrophosphate.10H₂O and made up to 120 ml with water. The pH was adjusted to pH=8 with dropwise addition of 20% phosphoric acid. The initial concentration of Pt as metal in the bath was 8.3 g/l.

Using a substrate of gritted steel and the following conditions: 1.90V, 070 mA, 80° C., pH=8, for 140 minutes, an attractive bright coating was obtained. Eventually a total weight of 0.4669 g of platinum plate was obtained.

Example 3

1.2 ml neat phosphoric acid was added dropwise with stirring to 50 ml of 20Q tetraammineplatinum(II) hydrogen phosphate solution until the pH was approximately 1. 2.4 g of tetrasodium pyrophosphate.10H₂O dissolved in 100 ml water was added to yield a final bath of pH 2. The initial concentration of Pt as metal in the bath was 10 g/l. Using a substrate of gritted steel, and plating conditions: 2.04V, 066 mA, 80° C., pH=2, plate time 1 hour, a bright deposit of 0.0428 g platinum was obtained, although there was vigorous bubbling from both anode and cathode during plating.

Example 4

1.35 g of tetraammineplatinum (II) hydrogen carbonate was dissolved in 120 ml water and melted pyrophosphoric acid was added dropwise until pH=1 was reached. The initial concentration of Pt as metal in the bath was 5.7 g/l. An attempt to plate gritted steel was unsuccessful due to extensive gas formation on the substrate. However, when 1.6 g tetrasodium pyrophosphate.10H₂O was added to the solution, gas formation ceased and the steel surfaces plated well and evenly under the conditions: 1.83V, 062 mA, pH=2, 80-85° C., plate time 1 hour, yielding 0.2571 g of bright Pt plate.

Example 5 (Comparative)

50 ml of 20Q tetraammineplatinum(II) hydrogen phosphate solution was diluted with water to give 120 ml containing 1 g Pt. The pH was maintained at 10-11 by periodic additions of 50% ammonia. A gritted steel substrate was plated under the conditions: 2.06V, 072 mA, 90-92° C., pH=10-11, plate time 1 hour, yielding a bright Pt coating of weight 0.1931 g.

Example 6

A plating bath was formed from 5.3 g potassium tetranitroplatinate(II) (Alfa Aesar), 0.5 ml of 45% ortho-phosphoric acid, 2.5 g of tetrapotassium pyrophosphate and 250 ml of water. The initial concentration of Pt as metal in the bath was 9 g/l. Using plating conditions of 1.37V, 065 mA, pH=8, 90° C., plate time 1 hour, an attractive mirror-bright plate was obtained on both sides of a polished brass substrate.

Example 7 Example 7a 8.3 g/l Pt Bath

175 ml of water was added with stirring to 125 ml of Johnson Matthey's 20Q tetraammineplatinum(II) hydrogen phosphate solution (20 g/l). 45% ortho-phosphoric acid was added to adjust the pH from 10 to 7 (approx. 0.5-0.75 ml). The solution was warmed and 2.5 g of tetrapotassium pyrophosphate added. A clear solution formed at about pH 8 and a leveller was added if desired (approx. 0.01-1 g). The bath was heated to 90° C., whereupon the bath was ready for plating.

Example 7b 10 g/l Pt Bath

As for Example 7a except that 150 ml of 20Q solution was used with 150 ml of water.

Example 7c 20 g/l Pt Bath

As for Example 7a except that 300 ml of 20Q solution used, no water and the masses of the phosphorus-containing components were doubled.

Example 8 Preparation of Tetraammineplatinum(II) Dihydrogen Pyrophosphate

Tetraammineplatinum(II) dihydrogen pyrophosphate [Pt(NH₃)₄][H₂P₂O₇] was prepared by reacting 1 mole of Pt(NH₃)₄(OH)₂ or Pt(NH₃)₄(HCO₃)₂ with 1 mole of pyrophosphoric acid, H₄P₂O₇ in water.

Preparation of Di(Tetraammineplatinum(II)) Pyrophosphate

Di[tetraammineplatinum(II)]pyrophosphate [Pt(NH₃)₄]₂[P₂O₇] was prepared by reacting 1 mole of Pt(NH₃)₄(OH)₂ or Pt(NH₃)₄(HCO₃)₂ with 0.5 mole of pyrophosphoric acid, H₄P₂O₇ in water.

Preparation of Na₂[Pt(NH₃)₄][H₂P₂O₇]

Na₂[Pt(NH₃)₄][H₂P₂O₇] was prepared by reacting 1 mole of Pt(NH₃)₄(OH)₂ or Pt(NH₃)₄(HCO₃)₂ with 1 mole of Na₂H₂P₂O₇ in water.

Example 8a 8.3 g/l Pt Bath

50 ml of water was added with stirring to 250 ml of tetraamineplatinum(II) dihydrogen pyrophosphate solution or di[tetraammineplatinum(II)]pyrophosphate (10 g/l). The solution was warmed and tetrapotassium pyrophosphate added until the pH increased from 3 to a pH between 5 and 8. A clear solution formed and a leveller was added if desired. The initial concentration of Pt as metal in the bath was approx. 8.3 g/l. The bath was heated to 90° C., whereupon the bath was ready for plating.

Example 8b 10 g/l Pt Bath

As for Example 8a except that 300 ml of tetraammineplatinum(II) dihydrogen pyrophosphate or di[tetraammineplatinum(II)]pyrophosphate solution at pH 3 and 10 g/l Pt as metal was used. Tetrapotassium pyrophosphate or sodium hydroxide was added to increase the pH to 7-8. A clear solution formed and a leveller was added if desired. The bath was heated to 90° C., whereupon the bath was ready for plating.

Example 9 Example 9a

A plating bath was formed from 250 ml tetraammineplatinum(II) hydrogen pyrophosphate solution at 10 g/l Pt and 50 ml of water. 5 g of tetrapotassium pyrophosphate was added to increase the pH from 3 to 7.5. The initial concentration of Pt as metal in the bath was 10 g/l. Using plating conditions of 1.13V, 072 mA, 90° C., pH=7.5, plate time 1 hour, a plaque was plated with 0.1798 g of a bright deposit of Pt.

When 0.04 g of the leveller 4-cyanopyridine was added to the plating bath, the shaped test part was plated with 0.03 g of levelled Pt in 60 minutes.

Example 9b

A plating bath was formed from 250 ml tetraammineplatinum(II) dihydrogen pyrophosphate solution at 10 g/l Pt and 50 ml of water. 5 g of tetrapotassium pyrophosphate was added to increase the pH from 3 to 7.5. The initial concentration of Pt as metal in the bath was 10 g/l. Using plating conditions of 1.10v, 071 mA, 90° C., pH=7.5, plate time 60 minutes, five polished brass plaques (both sides at 3.5×2.5 cm) were successively plated for 60 minutes each.

Plaque no. Quantity of Pt plated/g Comments 1 0.2208 Bright reflective appearance 2 0.2349 Bright reflective appearance 3* 0.3613 Bright matt appearance 4^(‡) 0.3125 Bright matt appearance 5 0.1911 Bright reflective appearance *Plated at 1.8v, 140 mA ^(‡)Plated at 1.3v, 100 mA

Example 9c

A plating bath was formed from 250 ml tetraammineplatinum(II) dihydrogen pyrophosphate solution at 10 g/l Pt and 50 ml of water. The initial concentration of Pt as metal in the bath was 10 g/l. No tetrapotassium pyrophosphate was added to the bath. Using plating conditions of 1.69V, 071 mA, 90° C., pH=4, plate time 1 hour, a polished brass plaque (both sides at 3.5×2.5 cm) was plated with 0.2018 g of a bright deposit of Pt. The pH of the bath rose to pH 5 during deposition.

Example 10

Using the conditions described in Examples 7 to 9, the following levellers were found to be useful in the plating baths of the present invention:

Levellers Sulfo-imines: Saccharin Sodium saccharine Potassium saccharine Calcium saccharine Pyrones: Coumarin Benzaldehydes and derivatives: Vanillin Ortho-vanillin Ethyl vanillin Vanillin acetate Methyl vallinate Vanillic acid 3-Methoxysalicylic acid Alkenyl compounds: Trans-1,4-Butendiol Cis-2-butene-1,4-diol 3-Butene-1,2-diol Diaminomaleonitrile Alkynyl compounds: 1,4-Butynediol 1,4-Butynediol diacetate Propargyl alcohol Nitrile compounds: 3-Hydroxypropionitrile 2-Hydroxypropionitrile Cyanoacetic acid Succinonitrile^(‡) Pyridyl compounds: 4-Cyanopyridinet^(†) 3-Cyanopyrdine^(⋄) 2-Cyanopyridine Iso-nicotinamide^(†) Nicotinamide^(⋄) Iso-nicotinaldehyde^(†) Nicotinaldehyde^(⋄) Iso-nicotinic acid Iso-nicotinic acid sodium salt Iso-nicotinic acid potassium salt Iso-nicotinic acid calcium salt Iso-nicotinic acid ammonium salt Nicotinic acid Nicotinic acid sodium salt Nicotinic acid potassium salt Nicotinic acid calcium salt Nicotinic acid ammonium salt Nicotine Methyl nicotinate N,N-Dimethylnicotinamide Trans-3-(3-pyridyl)acrylic acid Trans-3-(4-pyridyl)acrylic acid Pyridine-3-sulfonic acid 4-(2-pyridylazo)resorcinol 2,2′-Bipyridyl 4,4′-Bipyridyl Quinoline Isoquinoline Aminopyrazoles: 3-Amino-1,2,4-triazole 3-Amino-1,2,4-triazole-5-carboxylic acid Polyalkylimines: Polyethyleneimine Ethoxylated polyethyleneimine (ethoxy PEI) ^(‡)Each nitrile group can convert over time to a —COON group via a —CONH₂ group under the conditions of the plating baths of the present invention. ^(†)Can convert over time to iso-nicotinic acid under the conditions of the plating baths of the present invention. ^(⋄)Can convert to nicotinic acid under the conditions of the plating baths of the present invention.

Example 11

A plating bath was formed from 125 ml of 20Q solution (20 g/l of platinum as metal), 175 ml of water, 0.7 ml of 40% phosphoric acid, 2.5 g of potassium pyrophosphate and 0.04 g of nicotinic acid N-oxide. The initial concentration of Pt as metal in the bath was 8.3 g/l. Using the plating conditions as detailed in the following table, two test parts (see FIG. 1) were successively plated.

Part Quantity of no. Plating conditions Pt plated/g Comments 1 1.96 V, 070 mA, 0.1419 g Even grey matt pH of bath = 8, appearance temperature of bath = 90° C., plating time = 110 mins 2 1.72 V, 048 mA, 0.2018 Even grey matt pH of bath = 8, appearance temperature of bath = 90° C., plating time = 120 mins

Example 12

Isonicotinamide, isonicotinic acid and nicotinic acid were tested as levellers in plating baths under the following conditions:

The plating bath was prepared from 125 ml of 20Q solution (20 g/l platinum as metal), 0.5-1 ml of 40% phosphoric acid, 2.5 g potassium pyrophosphate, 175 ml water and 0.04 g of leveller.

The plating conditions were 072 mA on a 12 sq. cm. shaped test part, pH 7.5-8.5 at 90° C.

Example Leveller Quantity of Pt plated 12a Isonicotinamide 0.0718 g after 1 hr; 0.3136 g after 4 hrs 12b Isonicotinic acid 0.0990 g after 1 hr; 0.3973 g after 4 hrs 12c Nicotinic acid 0.2000 g after 98 mins

Example 13

1 ml of HReO₄ solution (75-80% HReO₄) was added to 125 ml of 20Q solution (20 g/l Pt metal) and 175 ml water which resulted in a white precipitate. 2.5 g of potassium pyrophosphate was added and the reaction mixture heated to 90° C. resulting in the dissolution of the white precipitate. The bath was used to plate a shaped part (see FIG. 1) at 90° C., 1.7V, 064 mA, pH 8.5 for 60 mins resulting in 0.1741 g of a bright silvery coating which was less bright and reflective than Pt alone. The coating is a platinum-rhenium alloy.

A second sample of polished brass (dimensions 4×2.5 cm) was plated in the bath to give 0.1980 g of alloy coating in 60 mins at 1.87V, 069 mA, 90° C. and pH 8.

A third sample of polished stainless steel (dimensions 4×2.5 cm) was plated in the bath to give 0.1710 g of alloy coating in 60 mins at 1.87V, 069 mA, 90° C. and pH 8.

Example 14

The effect of selected levellers on the platinum plating distribution was assessed using a shaped part as shown in FIG. 1. The part was plated, cut it in half and then after mounting and polishing the plated thickness at eight points around the part was measured (see FIG. 2).

The distribution plot for commercially available Q Salt shows an increased thickness at locations 2, 4, 6 and 8 together with a reduces thickness at locations 3 and 7. All the other plots show less variation due to the presence of the named levellers.

Example 15

A stock solution was prepared from 300 ml of 20Q solution (pH 10-11 and 20 g/l of Pt as metal) and 50% phosphoric acid was added dropwise with stirring until the pH was lowered to 3.

A platinum plating bath was prepared from 50 ml of the stock solution, 3 g sodium tripolyphosphate (85% tech grade) and 120 ml water. The pH of the bath was 7.

A steel plaque (dimensions 6×2.5 cm) was plating using the conditions 1.66V, 076 mA, 80-85° C., pH 7 to give 0.2020 g of a bright platinum plate in 60 minutes. 

1-30. (canceled)
 31. An aqueous platinum electroplating bath for depositing a coating of platinum on a substrate, the bath comprising: a) at least one platinum plating salt or complex; and b) a source of polyphosphate anions, and wherein the bath has a pH in the range from about 2 to about 9 when it is in use or ready for use.
 32. A bath according to claim 31, wherein the platinum plating salt or complex is selected from the group consisting of diammine dinitroplatinum(II), tetraammineplatinum(II) hydrogen orthophosphate, tetraamineplatinum(II) nitrate, tetraammineplatinum(II) hydrogen carbonate, tetraammineplatinum(II) hydroxide and tetraammineplatinum(II) sulphate.
 33. A bath according to claim 31, wherein the platinum plating salt or complex is selected from the group consisting of alkali metal hexahydroxyplatinates(IV), alkali metal tetranitroplatinates(II), alkali metal salts of hydrogen hexachloroplatinate(IV), alkali metal salts of hydrogen dinitrosulphatoplatinate(II), alkali metal tetrahaloplatinates(II) and tetraamineplatinum(II) halides.
 34. A bath according to claim 31, wherein the source of polyphosphate anions (a) is an alkali metal salt, alkaline earth metal salt or ammonium salt of a polyphosphoric acid, or a mixture thereof; (b) is selected from the group consisting of disodium pyrophosphate dibasic, dipotassium pyrophosphate dibasic, tetrasodium pyrophosphate, tetrasodium pyrophosphate decahydrate, tetrapotassium pyrophosphate, potassium tripolyphosphate, sodium hexametaphosphate, lithium hexametaphosphate, lithium hexametaphosphate.6H₂O, potassium hexametaphosphate, potassium pyrophosphate, sodium phosphate or a mixture thereof; or (c) is a polyphosphoric acid.
 35. A bath according to claim 31, wherein the source of platinum ions and the source of polyphosphate anions is a platinum polyphosphate salt or complex, optionally selected from the group consisting of tetraammineplatinum(II) dihydrogen pyrophosphate, di[tetraammineplatinum(II)]pyrophosphate, Na₂[Pt(NH₃)₄][H₂P₂O₇] and mixtures thereof.
 36. A bath according to claim 31, wherein the platinum ion concentration is about 1 to about 30 g/litre, and/or wherein the polyphosphate ion concentration is about 0.1 to about 90 g/litre.
 37. A bath according to claim 31 further comprising at least one leveller, wherein the leveller optionally comprises at least one unsaturated carbon-carbon or unsaturated carbon-heteroatom bond.
 38. A bath according to claim 37, wherein the leveller is selected from the group consisting of at least one: a) substituted or unsubstituted saccharine or salt thereof; b) substituted or unsubstituted benzopyranone; c) substituted or unsubstituted benzaldehyde or derivative thereof; d) substituted or unsubstituted alkene provided the alkene is not ethylene; e) substituted or unsubstituted alkyne provided the alkyne is not acetylene; f) substituted or unsubstituted alkylnitrile; g) substituted or unsubstituted pyridine or addition salt thereof; h) substituted or unsubstituted triazole; and i) substituted or unsubstituted pyridinium salt.
 39. A bath according to claim 37, wherein the leveller is: (a) a compound of formula (1) or salts thereof:

wherein m is 0, 1, 2, 3 or 4; each R₁ is independently an unsubstituted C₁-C₁₀ alkyl group; R₂ is selected from the group consisting of H, unsubstituted C₁-C₁₀ alkyl, an alkali metal ion and an alkaline earth metal ion; or (b) a compound of formula (2a), (2b) or (2c):

wherein n is 0, 1, 2, 3 or 4; p is 0, 1 or 2; each R₁₀ and R₁₁ is independently selected from an unsubstituted C₁-C₁₀ alkyl group; or (c) a compound of formula (3a) or (3b):

wherein R₂₀ is selected from the group consisting of H and —OR₂₃; and R₂₁ and R₂₂ are independently selected from the group consisting of H, —C(O)R₂₄ and unsubstituted C₁-C₁₀-alkyl; and R₂₃ and R₂₄ are independently selected from the group consisting of H and unsubstituted C₁-C₁₀-alkyl; or (d) a compound of formula (4):

wherein each R₃₀, R₃₁, R₃₂ and R₃₃ is independently selected from the group consisting of H, unsubstituted C₁-C₁₀-alkyl, substituted C₁-C₁₀-alkyl, —CO₂R₃₄, —NR₃₄R₃₅, —CONR₃₄R₃₅ and —CN, provided that R₃₀, R₃₁, R₃₂ and R₃₃ are not all H, wherein the substituents are selected from the group consisting of at least one —OH, —CO₂R₃₆, —OC(O)R₃₆, —NR₃₆R₃₇, —CONR₃₆R₃₇, —CN, —SO₃ ⁻Na⁺ and —SO₃ ⁻K⁺; R₃₄ and R₃₅ are independently selected from the group consisting of H and unsubstituted C₁-C₁₀-alkyl; and R₃₆ and R₃₇ are independently selected from the group consisting of H and unsubstituted C₁-C₁₀-alkyl; or (e) a compound of formula (5):

wherein R₄₀ and R₄₁ are independently selected from the group consisting of H, unsubstituted C₁-C₁₀-alkyl and substituted C₁-C₁₀-alkyl, provided that R₄₀ and R₄₁ are not both H, wherein the substituents are selected from the group consisting of at least one of —OH, —CO₂R₄₂, —OC(O)R₄₂, —NR₄₂R₄₃, —CONR₄₂R₄₃, —CN, —SO₃ ⁻Na⁺ and —SO₃ ⁻K⁺; R₄₂ and R₄₃ are independently selected from the group consisting of H and unsubstituted C₁-C₁₀-alkyl; or (f) a compound of formula (6): R₅₀—CN  (6) wherein R₅₀ is a substituted or unsubstituted and the substituents are selected from the group consisting of at least one of —OR₅₁, —CO₂R₅₁, —OC(O)R₅₁, —NR₅₁R₅₂ and —CN; and wherein R₅₁ and R₅₂ are independently selected from the group consisting of H and unsubstituted C₁-C₁₀-alkyl; or (g) a compound of formula (7a), (7b) or (7c):

wherein R₆₀ and R₆₁ are independently selected from the group consisting of —OH, —CN, —CONR₆₂R₆₃, —CO₂R₆₂, —COR₆₃, N-(unsubstituted C₁-C₁₀-alkyl)-pyrrolidinyl, unsubstituted C₁-C₁₀-alkyl, substituted C₁-C₁₀-alkyl, unsubstituted C₂-C₁₀-alkenyl, substituted C₂-C₁₀-alkenyl, —SO₂—R₆₃, —N═N-(unsubstituted C₆-C₁₀-aryl), —N═N-(substituted C₆-C₂₀-aryl), unsubstituted pyridyl, substituted pyridyl, wherein the substituents are independently selected from the group consisting of at least one of —CN, —CONR₆₄R₆₅, —COR₆₅, —CO₂R₆₄, —OH, —NR₆₄R₆₅ and ═NR₆₄; R₆₂ is selected from the group consisting of H, —OH and unsubstituted C₁-C₁₀-alkyl; R₆₃ is selected from the group consisting of H, —OH, unsubstituted C₁-C₁₀-alkyl, unsubstituted C₁-C₁₀-alkyl-CO₂H, —NH₂, —NH(unsubstituted C₁-C₁₀-alkyl), —N(unsubstituted C₁-C₁₀-alkyl)₂; R₆₄ is selected from the groups defined for R₆₂; R₆₅ is selected from the groups defined for R₆₃; each x is 0, 1, 2 or 3; and each y is 0, 1, 2, 3 or 4; or (h) a compound of formula (8):

wherein R₇₀ is selected from a group consisting of H, —CO₂R₇₂ and —NR₇₂R₇₃; R₇₁ is selected from a group consisting of H and unsubstituted C₁-C₁₀-alkyl; R₇₂ and R₇₃ are independently selected from the group consisting of H and unsubstituted C₁-C₁₀-alkyl; one of X₁ and X₂ is C—R₇₄ and the other of X₁ and X₂ is N; and R₇₄ is selected from a group as defined for R₇₀; or (i) a compound of formula (9a), (9b) or (9c):

wherein R₆₀ and R₆₁ are independently selected from the group consisting of —OH, —CN, —CONR₆₂R₆₃, —CO₂R₆₂, —COR₆₃, N-(unsubstituted C₁-C₁₀-alkyl)-pyrrolidinyl, unsubstituted C₁-C₁₀-alkyl, substituted C₁-C₁₀-alkyl, unsubstituted C₂-C₁₀-alkenyl, substituted C₂-C₁₀-alkenyl, —SO₂—R₆₃, —N═N-(unsubstituted C₆-C₁₀-aryl), —N═N-(substituted C₆-C₂₀-aryl), unsubstituted pyridyl, substituted pyridyl, wherein the substituents are independently selected from the group consisting of at least one —CN, —CONR₆₄R₆₅, —COR₆₅, —CO₂R₆₄, —OH, —NR₆₄R₆₅ and ═NR₆₄; R₆₂ is selected from the group consisting of H, —OH and unsubstituted C₁-C₁₀-alkyl; R₆₃ is selected from the group consisting of H, —OH, unsubstituted C₁-C₁₀-alkyl, unsubstituted C₁-C₁₀-alkyl-CO₂H, —NH₂, —NH(unsubstituted C₁-C₁₀-alkyl), —N(unsubstituted C₁-C₁₀-alkyl)₂; R₆₄ is selected from the groups defined for R₆₂; R₆₅ is selected from the groups defined for R₆₃; R₈₂ is selected from the group consisting of —O⁻ and unsubstituted C₁-C₁₀-alkyl; Z is a counterion when R₈₂ is an unsubstituted C₁-C₁₀-alkyl; each x is 0, 1, 2 or 3; and each y is 0, 1, 2, 3 or 4; or (j) at least one substituted or unsubstituted polyalkyleneimines.
 40. A bath according to any claim 31, further comprising one or more other platinum group metal or base metal plating salts or complexes.
 41. A bath according to claim 31, wherein the rate of plating is about ≧0.5 microns thickness of platinum or platinum alloy per hour.
 42. A bath according to claim 31, wherein the bath is used at temperatures from about room temperature to about 100° C.
 43. A bath according to claim 31 further comprising one or more brighteners, surfactants or wetting agents.
 44. A platinum salt which is tetraammineplatinum(II) dihydrogen pyrophosphate, di[tetraammineplatinum(II)]pyrophosphate or Na₂[Pt(NH₃)₄][H₂P₂O₇].
 45. A method for plating platinum or a platinum alloy onto a substrate, comprising: providing an aqueous platinum electroplating bath according to claim 31; and plating the platinum or platinum alloy onto the substrate using the bath.
 46. A bath according to claim 32, wherein the source of polyphosphate anions (a) is an alkali metal salt, alkaline earth metal salt or ammonium salt of a polyphosphoric acid, or a mixture thereof; (b) is selected from the group consisting of disodium pyrophosphate dibasic, dipotassium pyrophosphate dibasic, tetrasodium pyrophosphate, tetrasodium pyrophosphate decahydrate, tetrapotassium pyrophosphate, potassium tripolyphosphate, sodium hexametaphosphate, lithium hexametaphosphate, lithium hexametaphosphate.6H₂O, potassium hexametaphosphate, potassium pyrophosphate, sodium phosphate or a mixture thereof; or (c) is a polyphosphoric acid.
 47. A bath according to claim 33, wherein the source of polyphosphate anions (a) is an alkali metal salt, alkaline earth metal salt or ammonium salt of a polyphosphoric acid, or a mixture thereof; (b) is selected from the group consisting of disodium pyrophosphate dibasic, dipotassium pyrophosphate dibasic, tetrasodium pyrophosphate, tetrasodium pyrophosphate decahydrate, tetrapotassium pyrophosphate, potassium tripolyphosphate, sodium hexametaphosphate, lithium hexametaphosphate, lithium hexametaphosphate.6H₂O, potassium hexametaphosphate, potassium pyrophosphate, sodium phosphate or a mixture thereof; or (c) is a polyphosphoric acid.
 48. A bath according to any claim 32, wherein the platinum ion concentration is about 1 to about 30 g/litre, and/or wherein the polyphosphate ion concentration is about 0.1 to about 90 g/litre.
 49. A bath according to any claim 33, wherein the platinum ion concentration is about 1 to about 30 g/litre, and/or wherein the polyphosphate ion concentration is about 0.1 to about 90 g/litre.
 50. A bath according to any claim 34, wherein the platinum ion concentration is about 1 to about 30 g/litre, and/or wherein the polyphosphate ion concentration is about 0.1 to about 90 g/litre. 